Field of the Invention
The present invention relates to a producing method for producing an optical substrate having a minute or fine pattern for scattering or diffracting light, by using a long film-shaped mold (elongated or long-length film-shaped mold); and an apparatus performing the producing method.
Description of the Related Art
The lithography method is known as a method for forming a fine pattern (minute pattern) such as a semiconductor integrated circuit. The resolution of a pattern formed by the lithography method depends on the wavelength of a light source, the numerical aperture of an optical system, etc., and a shorter wavelength light source is desired so as to respond to the demand for miniaturized devices in the recent years. Any short wavelength light source is, however, expensive and is not easily developed, and any optical material allowing such short wavelength light passing therethrough needs to be developed, as well. Further, a large sized optical element is required for producing a pattern with a large area by means of the conventional lithography method, which is difficult both technically and economically. Therefore, a new method for forming a desired pattern having a large area has been considered.
The nano-imprint method is known as a method for forming a fine pattern without using any conventional lithography apparatus. The nano-imprint method is a technique capable of transferring a pattern in nano-meter order by sandwiching a resin between a mold (die) and a substrate. As the nano-imprint method, the thermal nano-imprint method, the photo nano-imprint method, etc. have been studied depending on materials to be used. Among the above-described methods, the photo nano-imprint method is composed of the following four steps of: (i) coating with a resin layer (application of a resin layer), (ii) pressing with a mold, (iii) photo-curing and (iv) releasing of the mold (mold-releasing). Thus, the photo nano-imprint method is excellent in that the nano-sized processing can be realized with such a simple process. In particular, since a photo-curable resin curable by being irradiated with light is used as the resin layer, a period of time required for a pattern transfer step is short and thus a high throughput can be expected. Accordingly, the nano-imprint method is expected to be practiced not only in the field of semiconductor device but also in many fields such as optical members like organic EL element, LED, etc.; MEMS; biochips; and the like.
For example, in the organic EL element (organic light emitting diode), a hole injected from a hole injecting layer and an electron injected from an electron injecting layer are each transported to a light emitting layer, then the hole and electron are recombined on an organic molecule in the light emitting layer to excite the organic molecule, thereby emitting light. Therefore, in a case that the organic EL element is used as a display device and/or an illumination device, the light from the light emitting layer is required to be efficiently extracted from the surface of the organic EL element. In order to meet this demand, it is known from Japanese Patent Application Laid-open No. 2006-236748 that a diffraction-grating substrate is provided on a light extraction surface of the organic EL element.
In order to produce a concave-convex pattern (concavity and convexity pattern) of a diffraction grating substrate for an organic EL element, the applicant of the present invention discloses a method in PCT International Publication No. WO2011/007878A1, the method including: applying a solution, obtained by dissolving a block copolymer satisfying a predetermined condition into a solvent, on a base member, and forming a micro phase separation structure of the block copolymer by using a self-organizing phenomenon (self-assembly phenomenon) of the block copolymer, so as to obtain a master block (metal substrate) having a fine and irregular concave-convex pattern formed therein. After obtaining a transferred pattern as a mold by dripping a mixture of a silicon-based polymer and a curing agent onto the obtained master block and then by performing curing therefor, a glass substrate coated with a curable resin is pressed against the transferred pattern and the curable resin is cured by irradiation with ultraviolet rays. By doing so, a diffraction grating in which the transferred pattern is duplicated is produced. Further, by stacking a transparent electrode, an organic layer, and a metal electrode on the diffraction grating, an organic EL element can be obtained.
However, in order to mass-produce the above-mentioned diffraction grating for the organic EL element, it is necessary to efficiently perform the pattern transfer onto a material such as a curable resin by using the transferred pattern as the mold.
Thus, there is a demand for a transfer process and a transfer apparatus which are suitable for mass-producing optical substrate, such as the diffraction-grating substrate, etc., usable for the organic EL element, etc., by using the nano-imprint method and with high throughput.
The photo-curable resin as described above generally has low heat resistance, and is decomposed and/or generate any yellowing at a high temperature. Thus, there is fear that a film having the minute pattern might be disintegrated in a case that any high-temperature treatment is included in a subsequent step. Further, the photo-curable resin has a low adhesion property to a glass substrate. Furthermore, in a case that the resin layer to which the pattern has been transferred is used for an element such as the organic EL element, there is fear that any impurity might be eluted from the resin layer to thereby adversely affect the element. Therefore, in order to mass-produce the optical substrate such as the diffracting-grating substrate for the organic EL element with high throughput by using the nano-imprint method, the material for forming the concave-convex pattern on the glass substrate and/or the material for the mold are also required to be optimized.
In view of the above situation, an object of the present invention is to provide a novel producing method and producing apparatus capable of mass-producing, with a high throughput, an optical substrate provided with a minute or fine concave-convex pattern which has a high adhesion property to the substrate, heat resistance, and weather resistance; and to provide a novel optical substrate obtained by the novel producing method and producing apparatus.